I have been away for a few days, and I see this thread is still going, which would be hard to believe except ... this is ScubaBoard, and we have so many really knowledgeable folks who are eager to share their knowledge and opinions.
@Isa.nerwen , I'm impressed you have continued to listen. We do mean well!
As I see it, Thailand is where one goes to party on the beach while taking a course to justify why they are there for so long. I do not believe Thailand is the best place to get quality dive training that will make one a better diver. I am guessing in your previous trips you did the partying thing, and maybe you have gotten that out of your system. But you seem intent to do this training in Thailand, and so, I say "why not."
Instructors cannot help you reach a skill level that they themselves have not attained. Unless your instructor is a tech diver, they are unlikely to care much about perfecting skills such as horizontal trim and controlled ascents (ie, buoyancy). Their attitude would not be wrong; for most recreational divers, even divemasters, tech-level performance is simply not needed, so why waste time with that? As a recreational diver, you don't really need to ascend with such good control that you could stop every 3 meters and hold that depth in perfect horizontal trim if you wished to. Indeed, maintaining horizontal trim is often counterproductive on a recreational dive, such as when you're drifting along a wall and you want to take in the view up and down the wall in all its majesty.
See above! Your instructor, unless they are also a tech diver AND a bit obsessive in how they teach the DM course, may simply react with a shrug or tell you your trim is just fine, and that would be completely understandable.
Sounds like a good idea to me. Try to work with an instructor who (1) is trained in and does tech diving on a regular basis and (2) who is willing to work with you to help you attain a tech level of performance. I would not count on just any instructor teaching an Intro-to-Tech course in which enough time is spent on honing performance. The curriculum of an intro to tech-type course likely also includes the mechanics of tech diving--the kit, etc.--and that is perhaps less relevant if your goal is simply to become a better, higher-performing recreational diver.
I took a course that some might characterize as an intro to tech type course (GUE Fundamentals), with the express intent of simply becoming a better recreational diver, and I was pleased with the results. Just as one (useful, I think) example, I learned to move toward whatever small creature or coral head I wanted to gaze at and arrest my forward motion with a small back-kick when I arrived at the distance I wanted to be at, then maintain my orientation and position in the water, perhaps just inches above the bottom, without excessive finning or stirring up the bottom. While enjoying the viewing, divers with less well-honed skills will sometimes arrive to see what I am looking at and flail around, unable to do what I describe. I'm not bragging--I'm still hardly the most skilled diver out there--but I can say these are really great skills for a recreational diver to have in their tool kit.